The present invention relates to a semiconductor laser device widely used in optical communication systems and optical sensor systems, such as, for example, communication, medical and industrial sensors, and a method for producing the same. In particular, the present invention relates to a semiconductor laser device used for a light source, for emitting light into an outside space, which is directly viewed by humans: for example, a light source for wireless communication, a light source for a sensor or the like. The present invention also relates to a method for producing such a semiconductor laser device, and an optical communication system and an optical sensor system using such a semiconductor laser device to provide guaranteed safety.
As an example of a conventional space-emission semiconductor light emitting device, FIG. 10 shows a space-emission semiconductor light emitting device disclosed in Japanese Laid-Open Publication No. 8-264885.
This semiconductor light emitting device has a structure in which a laser chip 1 is soldered to a metal heat sink 6 and a tip area of the laser chip 1 and an electrode (lead frame) 3 are electrically connected to each other by a wire 3a. The heat sink 6 is integrated on a stem 8. The laser chip 1 is sealed by a cap 9 having a diffusive plate 5 bonded thereto.
In such a semiconductor light emitting device, light emitted from the laser chip 1 radiates toward the diffusive plate 5. The direction and phase of the light are disturbed by the diffusive plate 5, and thus the light is scattered. In this manner, the coherency of the radiating light is reduced so that safety for the eyes of a viewer is guaranteed, before the light is released to the outside space.
According to another known method for realizing a light-diffusive function, a laser chip is covered with a molded mixture of a silica-based resin and an epoxy-based resin. By this method, the laser light is scattered due to a difference in refractive index between the epoxy-based resin and the silica-based resin, thereby reducing the coherency of the radiating light. A material containing a small amount of silica-based resin mixed with an epoxy-based resin is generally used since the epoxy-based resin is light-transmissive and the silica-based resin is not light-transmissive.
In the case where a semiconductor device including the diffusive plate 5 shown in FIG. 10 is used, problems occurs such as, for example, the diffusive plate is broken when an apparatus having the semiconductor device mounted thereon is dropped or the like. As a result, a high output of coherent light can be undesirably released to the outside space.
In the case where the laser chip is covered with a molded resin containing a light-diffusive material, for example, a resin containing a silica-based resin, the following or other problems occur. Due to the high moisture permeability of the silica-based resin, wires are worn and broken or end surfaces of the laser chip are deteriorated over time. This reduces the reliability.
The present invention made to solve these problems of conventional devices has an objective of providing a semiconductor laser device for guaranteeing safety for the eyes by preventing a high output of coherent light from being released to the outside space so as to improve reliability, a method for producing the same, and an optical communication system and an optical sensor system using the same.
A semiconductor laser device according to the present invention includes a resin section in which a light-diffusive surface thereof is entirely or partially roughened, or a surface thereof facing a laser chip is entirely or partially roughened. The roughened portion of the resin section diffuses light so as to reduce coherency of the radiating light. Thus, the above-described objective is achieved.
A semiconductor laser device according to the present invention includes a resin section for integrating a container accommodating a laser chip and a sealing member having a light-diffusive function. The sealing member diffuses light so as to reduce coherency of the radiating light. Thus, the above-described objective is achieved.
A semiconductor laser device according to the present invention includes a resin section formed of a resin material in which a different resin material having a different refractive index from that of the first resin material is mixed or a resin section formed of a birefringent resin material, the resin section being provided so as not to contact a laser chip. The resin section diffuses light so as to reduce coherency of the radiating light. Thus, the above-described objective is achieved.
A semiconductor laser device according to the present invention includes a resin section, a portion of which is an area formed of a resin material in which a different resin material having a different refractive index from that of the first resin material is mixed or an area formed of a birefringent resin material, the area being provided so as not to contact a laser chip. The area diffuses light so as to reduce coherency of the radiating light. Thus, the above-described objective is achieved.
Preferably, an area at a center and the vicinity thereof of a surface of the resin section facing the laser chip is a curved surface having a light outgoing point of the laser chip as the center of curvature.
Preferably, a peripheral area of the surface of the resin section facing the laser chip is a curved surface having the center of curvature on a side opposite to the laser chip.
Preferably, an area at a center and in the vicinity of a surface of the resin section facing the laser chip is substantially flat and a peripheral area is convex.
Preferably, a normal to at least a light passing area of the convex area of the resin section is at an angle of larger than 0xc2x0 and 3xc2x0 or smaller with respect to a peak vector of a light beam emitted from the laser chip.
Preferably, an area at a center and in the vicinity of a surface of the resin section facing the laser chip is substantially flat and a peripheral area is roughened.
The resin section may be formed of a birefringent resin material.
A semiconductor laser device according to the present invention includes a resin section formed of a birefringent resin material and a laser chip integrated together, wherein the resin section diffuses light so as to reduce coherency of the radiating light. Thus, the above-described objective is achieved.
Preferably, a relationship of xcex94n/n2 greater than 0.0015 is fulfilled, where An is an inherent birefringence value of light having an oscillating wavelength of the semiconductor laser device and n is an average refractive index for a light having the oscillating wavelength.
The birefringent resin material may be one material, a polymer blend of at least two materials, or a polymer blend containing at least one material of polyimide, polycarbonate, polyallylate, polyethersulfone, polyphenylene sulfide, polyphenylene oxide, polyallyl sulfone, polyamideimide, polyolefin, polyacrylonitrile, cellulose and polyester.
The birefringent resin material may be an aromatic polyester.
The aromatic polyester may be polyallylate or polycarbonate.
The aromatic polyester may be polyallylate obtained from a divalent phenol compound represented by chemical formula (I) and an aromatic dicarboxylic acid or polycarbonate obtained from the phenol compound and phosgene: 
A method for producing a semiconductor laser device according to the present invention produces a semiconductor laser device including a resin section in which a light-diffusive surface thereof is entirely or partially roughened, or a surface thereof facing a laser chip is entirely or partially roughened. The method includes the steps of immersing a laser chip or a container accommodating a laser chip in a resin material; and curing the resin material and roughening a corresponding portion. Thus, the above-described objective is achieved.
A method for producing a semiconductor laser device produces a semiconductor laser device including a resin section in which a light-diffusive surface thereof is entirely or partially roughened, or a surface thereof facing a laser chip is entirely or partially roughened. The method includes the steps of immersing a laser chip or a container accommodating a laser chip in a resin material and curing the resin material: and roughening a corresponding portion of the cured resin material. Thus, the above-described objective is achieved.
The step of roughening the intended portion of the cured resin material may be performed by etching, polishing, or pressing a mold having a rough surface to the corresponding portion.
An optical communication system according to the present invention includes a semiconductor laser device according to the present invention. Thus, the above-described objective is achieved.
An optical sensor system according to the present invention includes a semiconductor laser device according to the present invention. Thus, the above-described objective is achieved.
Hereinafter, the function of the present invention will be described.
According to the present invention, as described later in Example 1, a light-diffusive surface of a resin section formed of a molded resin or the like is entirely or partially roughened. Alternatively, as described later in Example 8, a surface of a resin section for integrating a glass cap to a cap, the surface facing a laser chip, is entirely or partially roughened. The roughened portion of the resin section can diffuse light so as to reduce coherency of the radiating light. Therefore, there is no undesirable possibility that breakage of a diffusive plate may prevent safety for the eyes or that a reliability of the semiconductor laser device is lowered by a silica-based resin, unlike the conventional devices.
A desired portion of the resin section can be easily roughened by immersing the laser chip in a resin material using a mold having a rough surface and then curing the resin material. Alternatively, a desired portion of the resin section can be easily roughened by curing the resin material and then etching, by polishing, or by pressing a mold having a rough surface to a corresponding portion of the resin section.
As described later in Example 12, the resin section can be formed of a birefringent resin material and a surface of the resin section can be roughened. In this case, the light-diffusive function of the resin material itself and the light-diffusive function provided by the roughening of the surface are combined to diffuse light more efficiently. Thus, a semiconductor laser device which is highly stable can be provided.
In another embodiment of the invention, as described later in Example 2, a container such as a cap for accommodating the laser chip and a sealing member having a light-diffusive function (glass cap) such as a diffusive plate or the like are integrated together by a resin section. Since the sealing member having the diffusive function is integrated with the resin, there is no undesirable possibility that breakage of the diffusive plate may prevent safety for the eyes or that the reliability of the semiconductor laser device is lowered by a silica-based resin, unlike the conventional devices.
In still another embodiment of the invention, as described later in Examples 2 through 4 example, a resin section formed of a resin material in which another resin material having a different refractive index from that of the first resin material is therein is provided. Light is diffused by a difference in refractive index between different materials contained in the resin section so as to reduce coherency of the radiating light. Thus, there is no undesirable possibility that breakage of the diffusive plate may prevent safety for the eyes, unlike the conventional devices. Since the laser chip is not in contact with the resin section, stress-derived strain or the like due to a change in environmental temperature is not generated. Even when a moisture permeable material such as a silica-based resin or the like is included, the reliability of the semiconductor laser device is not reduced.
Alternatively, as described later in Examples 9 through 11, a resin section formed of a birefringent resin material is provided. As such, the refractive index is varied in accordance with the polarization state of the incident light. The light is diffused by the difference in refractive index, and thus coherency of the radiating light can be reduced. Therefore, there is no undesirable possibility that breakage of the diffusive plate may prevent safety for the eyes, unlike the conventional devices. There is no problem either that the reliability of the semiconductor laser device is reduced due to the use of a silica-based resin.
In the case where an area at the center and in the vicinity of a surface of the resin section, the surface facing the laser chip, is a curved surface having a light outgoing point of the laser chip as the center of curvature, the output efficiency of the S polarization can be increased as described later in Example 5.
In the case where an area at the center and in the vicinity of a surface of the resin section, the surface facing the laser chip, is formed to be a curved surface having a light outgoing point of the laser chip as the center of curvature, and a peripheral area is formed to be a curved surface having the center of curvature on the opposite side to the laser chip, the light output efficiency can be increased in accordance with the polarization state of the light as described later in Example 7.
In the case where an area at a center and in the vicinity of a surface of the resin section, the surface facing the laser chip, is formed to be substantially flat and a peripheral area is formed to be convex, light can be output from the diffusive plate more efficiently as described later in Example 6 or 2.
In the case where the normal to at least a light passing area of the convex area of the resin section is at an angle of larger than 0xc2x0 and 3xc2x0 or smaller with respect to a peak vector of a light beam emitted from the laser chip, the light output efficiency is further improved as described later in Example 6.
In the case where an area at a center and in the vicinity of a surface of the resin section, the surface facing the laser chip, is formed to be substantially flat and a peripheral area is roughened, the light output efficiency can be easily improved without detailed design as described later in Example 8.
In still another embodiment of the invention, a resin section includes an area formed of a resin material in which another resin material having a different refractive index from that of the first resin material is mixed as described later in Example 1. The light is scattered by the difference in refractive index between the materials contained in the area so as to reduce the amount of radiating light. As such, there is no undesirable possibility that breakage of the diffusive plate may prevent safety for the eyes, unlike the conventional devices. Since the area containing a material having a different refractive index is not in contact with the laser chip, stress-derived strain due to a change in environmental temperature is not generated. Even when a moisture permeable material such as a silica resin or the like is contained in the area, the reliability of the semiconductor laser device is not reduced.
Alternatively, as described later in Example 1, a resin section including an area formed of a birefringent resin material is provided. Since light is diffused by a refractive index which varies in accordance with the polarization state of the incident light, coherency of the radiating light can be reduced. There is no undesirable possibility that breakage of the diffusive plate may prevent safety for the eyes, unlike the conventional devices. There is no problem either that the reliability of the semiconductor laser device is reduced by a silica-based resin, unlike the conventional devices.
In still another embodiment of the invention, as described later in Example 10, a resin section formed of a birefringent resin material and a laser chip are integrated together. Since light is diffused by a refractive index which varies in accordance with the polarization state of the incident light, coherency of the radiating light can be reduced. There is no undesirable possibility that breakage of the diffusive plate may prevent safety for the eyes, unlike the conventional devices. Since the birefringent resin material is not moisture permeable, unlike a silica resin or the like, the laser chip can be directly immersed in the birefringent resin material without first curing another resin material.
As described later in Example 9, a birefringent resin material provides a sufficient light-diffusive function as long as the birefringent resin material fulfills the relationship of xcex94n/n2 greater than 0.0015 where xcex94n is an inherent birefringence value of a light having an oscillating wavelength of the semiconductor laser device and n is an average refractive index for a light having the wavelength.
Resin materials as the birefringent resin material includes polyimide, polycarbonate, polyallylate, polyethersulfone, polyphenylene sulfide, polyphenylene oxide, polyallyl sulfone, polyamideimide, polyolefin, polyacrylonitrile, cellulose and polyester. A polymer blend of at least two of these materials, or a polymer blend containing at least one of these materials may be used. As described in Examples 9 and 10, light can be diffused using the birefringence of these resin materials. In addition, the light output efficiency can be improved due to the high transparency thereof.
As the birefringent resin material, an aromatic polyester may be used as described in Examples 11 and 12. Aromatic polyesters usually have an inherent high level of birefringence. Most of the aromatic polyesters have a relatively high heat resistance and are colorless and highly transparent. Representative aromatic polyesters having a high level of birefringence and a superb transparency include polyallylate and polycarbonate. Especially, polyallylate obtained from a divalent phenol compound represented by chemical formula (I) and an aromatic dicarboxylic acid or polycarbonate obtained from a divalent phenol compound represented by chemical formula (I) and phosgene are preferable. 
A representative aromatic polyester is, for example, a polyester using 9,9-bis(4-hydroxyphenyl)-fluorene represented by chemical formula (II) and disclosed in Japanese Laid-Open Publication No. 5-11115 as a divalent phenol compound. 
A three-dimensional (crosslinked) aromatic polyester can be used by adding a small amount of a trivalent phenol compound or aromatic tricarboxylic acid to the above aromatic polyester. Such a three-dimensional aromatic polyester improves the mechanical strength of the molded resin.
A semiconductor laser device according to the present invention guarantees safety for the eyes and has a satisfactory reliability. Such a semiconductor laser device can be preferably used for a laser beam which is directly viewed by humans in the fields of wireless optical communication, optical sensor systems and the like.